在javascript中返回！1 [英] return !1 in javascript

问题描述

我刚刚遇到了一个JavaScript函数，它有 return！1

我只是想知道这实际上意味着什么？

为什么你会返回！1 或 return！0

请问有人请解释一下这是什么意思？

碰到：

pre $ 函数convertStringToBoolean（a）{
typeof a ==string&& （a = a.toLowerCase（））;
switch（a）{
case1：
casetrue：
caseyes：
casey：
case 1：
case！0：
return！0;
default：
return！1
}
}


感谢提前！

解决方案

return！1 表示 return false 和 return！0 - 返回true 。在规范中 - 当您放置时， 11.4.9逻辑非运算符 - ！在前面结果评估为布尔值，并且返回相反的结果。

例子：

  var a = 1，b = 0; 
 var c = a || b; 
 alert（c =+ c ++ typeof c）; //这里c将数字
 a =！0，b =！1; 
 c = a || b; 
 alert（c =+ c ++ typeof c）; //这里是布尔
  

我主要在通过谷歌优化器传递的代码中看到这一点。我认为这主要是为了达到代码的简短性。

当需要布尔结果时经常使用它 - 您可能会看到类似于的东西！ ！（表达式）。例如，在jQuery中搜索。

I have just come across a function in javascript which has return !1

I was just wondering what this actually meant?

Why would you return !1 or return !0

Could someone please explain what it means please?

Here is the function that I came across:

function convertStringToBoolean(a) {
    typeof a == "string" && (a = a.toLowerCase());
    switch (a) {
    case "1":
    case "true":
    case "yes":
    case "y":
    case 1:
    case !0:
        return !0;
    default:
        return !1
    }
}

Thanks In advance!

解决方案

return !1 means return false and return !0 - return true. In the specification - 11.4.9 Logical NOT Operator - when you place ! in front the result is evaluated as Boolean and it the opposite is returned.

Example:

var a = 1, b = 0;
var c = a || b;
alert ( "c=" + c + " " + typeof c ); // here c will be number
a = !0, b = !1;
c = a || b;
alert ( "c=" + c + " " + typeof c ); // here it will be boolean

I mostly see this in a code passed through google's optimizer. I think it is mostly done to achieve shortness of the code.

It is often used when boolean result is needed - you may see something like !!(expression). Search in jQuery, for example.

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